A video posted online on Tuesday, purportedly by the Islamic State extremist group, depicted a black-clad militant with a knife threatening to kill two Japanese hostages within 72 hours unless the government in Tokyo paid a ransom of $200 million.

The video, which could not immediately be verified independently, showed two men, identified as Kenji Goto and Haruna Yukawa, kneeling on a rocky hillside, with the masked militant standing between them.

The militant linked the ransom demand to a Japanese offer of assistance to enemies of the Islamic State, also known as ISIS and ISIL, which controls a large amount of territory stretching from Syria into Iraq. The group says it is seeking to establish an Islamic caliphate and has previously shown videos of the beheading of two Americans, James Foley and Steven J. Sotloff, and two Britons, David Cawthorne Haines and Alan Henning.